Systems designed to monitor and/or record the installation process of a pile are known in the art. In this respect, Likins U.S. Pat. No. 5,978,749, discloses a pile installation recording system and is incorporated by reference herein and forms part of the specification of this application. More particularly, the Likins Patent discloses a pile installation recording system for both driven piles and auger-cast piles. The disclosed system can record a variety of parameters or data received from one or more sensing devices that are either attached to the pile, attached to the rig, or in a measurement range from the rig and/or the pile. These sensing devices can be any sensing devices known in the art and can be used to determine a wide range of parameters including, but not limited to, sensing the depth of a driven pile or the depth of an auger in an auger-cast pile.
However, while Likins has been found to be a very effective system in the field, applicant has found that the depth measurement device of Likins has its limitations which for years went unresolved. In this respect and with reference to FIG. 3 of Likins, the sensing device in Likins that is used to determine the depth of the pile and/or auger is joined to line 56 by a three-roller system. While not shown, this three-roller system is supported by the structure of rig 10, but which engages line 56 at or near the boom 12 of rig 10. The three roller system includes an encoder wheel 52. Further, in order to account for the movement of the wire as it is unwound from line real or drum 54, the roller system is joined to a fixed rod (not shown) having a linear bearing configured to allow lateral motion of the measurement system while the wire is unwound. As is known if the art, the wire being unwound from a roll or drum of wire can have significant lateral movement in that the wire is wound across the entire surface of the drum supporting the wire. While the linear bearing arrangement is effective in handling the lateral movement of the wire, it is not effective in handling the changes in load in the direction of line 56 wherein it has been found that the support rod, that is used to support the linear bearing, often deforms or fails in use. In either case, this condition adversely affects the accuracy of the depth sensor and the failure of the system in the field can cause downtime for the pile installation process.
In addition, in that many rigs are not owned by the operator, it is often difficult or impossible to convince the rig operator to weld a support bar to the rig, which is necessary to operate this type of sensing system. These rigs can cost hundreds of thousands of dollars, if not millions of dollars, wherein the owners of the rig are often hesitant to allow the types of modifications to the boom structure of the rig which are necessary to support this sensing system.
Even if the owner of the rig can be convinced to weld the necessary fixed bar to the boom, the sensing device shown in Likins has been found to have issues with accuracy for several reasons. One such reason is the way in which the wire is pinched between the three-roller system. In this respect, the wire passes through the fixed three-roller system wherein two of the rollers are in line with the wire on one side of the wire and the third roller (encoder wheel 52) is centered between the axes of the first two rollers wherein the center roller must deflect the wire as it passes therethrough such that a portion of the wire arcs around the encoder wheel. While this deflection about the encoder wheel can be accounted for if it remains constant, it has been found that it changes as the tension of the wire changes. It is difficult to account for the amount of wrap about this encoder wheel wherein the system inherently produces some level of error.
In addition, while FIG. 3 of Likins shows the line 56 to extending vertically between pulley 58 and gearbox or hammer cage 20, this line often extends from pulley 58 at an angle toward gearbox/hammer cage 20. In that the line is not extending in the vertical plane, the angle relative to the gearbox or hammer cage must be factored into the data to determine the actual vertical movement of the cage relative to the leads of the rig. Again, if the angle relative to the cage was constant, this adjustment to the data could be easily calculated. However, the distance between pulley 58 and cage 20 affects the relative angle of the line wherein this angle changes as the cage is displaced away from the pulley. As can be appreciated, it is difficult to account for this ever-changing angle, which is especially true in that each rig can have a different angle and/or a different angle change. As a result, it has been found that this system works adequately for short piles; however, the system becomes less and less accurate as the pile length increases.
Yet another problem found with the depth measurement system disclosed in the prior art is that the data produced by the system can be corrupted if the line is allowed to go slack. In that the measurement system is joined to the line, the line itself becomes a variable that must be maintained as a constant. A slack condition in this line affects this constant and can produce error. Moreover, if this slack condition is not noticed, the error in the data may not be known, which would result in a less accurate data set for the pile installation period. Depending on the frequency of the slack condition, and the other factors discussed above, the resulting data could be corrupted enough to prevent its use in evaluating the structural integrity of the installed pile.
Over the years, attempts have been made to overcome the shortcomings of the depth measurement system in Likins in order to produce more accurate data. One such attempt was to use a spring loaded real (similar to a tape measure) that is joined between a fixed point on the rig and the hammer cage or gearbox. This separated the sensing device from line 56 thereby eliminating the variables associated with the movement of this line. However, this device was found to have its own problems, which prevented its effective use in the field. In this respect, the system is heavy and expensive, weighing over 200 pounds, and produces yet another wire on the rig, which must be managed. As is known in the art, the installation process of a pile (whether it is a driven pile or an auger-cast pile), can be harsh and have negative impacts on sensing systems and wire structures. Further, with respect to driven piles, the system is constantly moving up and down to hammer a pile into the ground. It has been found, that this real system can often get tangled and in the way of other structures of the rig wherein its effectiveness has been found to be limited.
In addition to Likins, U.S. Pat. No. 6,533,502 to McVay is also incorporated by reference and forms part of this specification. The McVay patent also discloses a system for the determination of pile parameters and includes at least one structure for measuring pile data. The system discloses a structure for measuring pile data that is disposed within a measurement range from a pile wherein a wireless transmitter is communicably connected to the structure for measuring pile data. As with Likins, the wireless transmitter for transmitting the pile data can be in connection with a remotely located receiver.
Another patent incorporated by reference and forming part of this specification is U.S. Pat. No. 6,301,551 to Piscalko. The Piscalko patent discloses a pile driving analyzer (PDA) which obtains, processes and/or stores pile driving data. The PDA is operable as an independent self-contained unit, or may be used in conjunction with a remote computer system. Position data indicative of the position of a pile, and pile data indicative of characteristics of a pile may be automatically input to the PDA. When used in conjunction with the remote computer system, the PDA may be controlled remotely by the remote computer system. Alternatively, the PDA may be controlled locally by an operator, and data acquired by the PDA provided to the remote computer system for monitoring and/or storage.